Melting and crystallization of colloidal hard-sphere suspensions under shear

Wu, Yuling; Derks, Didi; Blaaderen, Alfons van; Imhof, Arnout

doi:10.1073/pnas.0812519106

Cited by 133 publications

(125 citation statements)

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“…Microscopy is an essential tool for identifying processes at the particle scale that control the bulk flow properties. Confocal imaging studies, for example, reveal that sheared hard-sphere colloidal crystals may change their local structure [26] or melt entirely [27], with the dynamics of crystallization and melting distinct from those under quiescent conditions [28]. Hardsphere colloidal glasses in shear flow exhibit strongly localized yielding [29], leading to shear-banding [30,31], or jamming and self-filtration [32].…”

Section: Introductionmentioning

confidence: 99%

Aqueous Colloid + Polymer Depletion System for Confocal Microscopy and Rheology

2018

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We developed a model depletion system with colloidal particles that were refractive index-and density-matched to 80 (w/w)% glycerol in water, and characterized the effect of interparticle interactions on the structure and dynamics of non-equilibrium phases. 2,2,2-trifluoroethyl methacrylate-co-tert-butyl methacrylate copolymer particles were synthesized following [1]. Particles were dispersed in glycerol/water solutions to generate colloidal suspensions with good control over electrostatic interactions and a moderately high background viscosity of 55 mPa·s. To probe the effects of charge screening and depletion attractions on the suspension phase behavior, we added NaCl and polyacrylamide (M w = 186 kDa) at various concentrations to particle suspensions formulated at volume fractions of φ = 0.05 and 0.3 and imaged the suspensions using confocal microscopy. The particles were nearly hard spheres at a NaCl concentration of 20 mM, but aggregated when the concentration of NaCl was further increased. Changes in the particle structure and dynamics with increasing concentration of the depletant polyacrylamide followed the trends expected from earlier experiments on depletion-driven gelation. Additionally, we measured the viscosity and corrected first normal stress difference of suspensions formulated at φ = 0.4 with and without added polymer. The solvent viscosity was suitable for rheology measurements without the onset of instabilities such as secondary flows or edge fracture. These results validate this system as an alternative to one common model system, suspensions of poly(methyl methacrylate) particles and polystyrene depletants in organic solvents, for investigating phase behavior and flow properties in attractive colloidal suspensions.

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Section: Introductionmentioning

confidence: 99%

Aqueous Colloid + Polymer Depletion System for Confocal Microscopy and Rheology

2018

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“…Sheared hard-sphere colloidal suspensions provide a simple system for probing many out-of-equilibrium structures. For example, sliding layers in sheared colloidal crystals (10,11), shear-induced crystallization of colloidal fluids (5), and formation of shear transformation zones-localized regimes of shear-induced structural rearrangement-in colloidal glasses (12) have been observed in such systems.…”

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“…Once driven out of equilibrium, a material can exhibit richer phases with many unexpected structures (2)(3)(4)(5)(6). However, the dynamics of these nonequilibrium phases are much less understood relative to their equilibrium counterparts (7)(8)(9).…”

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Assembly of vorticity-aligned hard-sphere colloidal strings in a simple shear flow

Cheng

Rice

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

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Colloidal suspensions self-assemble into equilibrium structures ranging from face-and body-centered cubic crystals to binary ionic crystals, and even kagome lattices. When driven out of equilibrium by hydrodynamic interactions, even more diverse structures can be accessed. However, mechanisms underlying out-of-equilibrium assembly are much less understood, though such processes are clearly relevant in many natural and industrial systems. Even in the simple case of hard-sphere colloidal particles under shear, there are conflicting predictions about whether particles link up into string-like structures along the shear flow direction. Here, using confocal microscopy, we measure the shear-induced suspension structure. Surprisingly, rather than flow-aligned strings, we observe log-rolling strings of particles normal to the plane of shear. By employing Stokesian dynamics simulations, we address the mechanism leading to this out-of-equilibrium structure and show that it emerges from a delicate balance between hydrodynamic and interparticle interactions. These results demonstrate a method for assembling large-scale particle structures using shear flows.colloids | shear-induced structure T he study of ordered structures and symmetries of equilibrium phases in condensed matter is central to our understanding of its various material properties (1). Once driven out of equilibrium, a material can exhibit richer phases with many unexpected structures (2-6). However, the dynamics of these nonequilibrium phases are much less understood relative to their equilibrium counterparts (7-9). Sheared hard-sphere colloidal suspensions provide a simple system for probing many out-of-equilibrium structures. For example, sliding layers in sheared colloidal crystals (10, 11), shear-induced crystallization of colloidal fluids (5), and formation of shear transformation zones-localized regimes of shear-induced structural rearrangement-in colloidal glasses (12) have been observed in such systems.The simplest and lowest ordered structure predicted to arise from sheared hard-sphere colloidal suspensions is a one-dimensional (1D) string structure, where particles link into strings under shear. This structure has received much attention since it was first found in a numerical simulation (13). Despite intensive study (13-23), however, there is still heated debate over whether such a structure exists in experiments (10,23,24) or is an artifact of certain numerical algorithms (20-23). In part, this controversy persists due to the lack of experimental techniques that provide direct visualization of the suspension structure. Since the string structure is predicted to exist in less concentrated suspensions below the crystallization threshold, previous scattering experiments, which average over large sample volumes, have not provided detailed information to unambiguously confirm or disprove the existence of this less regular structure (10,24). Here, by employing fast confocal microscopy, we show that sheared hardsphere colloidal suspensions form strings a...

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“…S hear is known to assist crystallization below the equilibrium freezing temperature in complex fluids like colloidal glasses (1,2), dense granular suspensions (3), polymer melts (4,5), micellar solutions of block copolymers (6), and multicomponent surfactant systems (7,8). Shear-driven crystallization is equally relevant for simple fluids like bulk metallic glasses (9), molecular liquids (10), and atomic systems (11).…”

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confidence: 99%

Reversible shear-induced crystallization above equilibrium freezing temperature in a lyotropic surfactant system

Rathee

Krishnaswamy

Pal

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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We demonstrate a unique shear-induced crystallization phenomenon above the equilibrium freezing temperature ðT o K Þ in weakly swollen isotropic ðL i Þ and lamellar ðL α Þ mesophases with bilayers formed in a cationic-anionic mixed surfactant system. Synchrotron rheological X-ray diffraction study reveals the crystallization transition to be reversible under shear (i.e., on stopping the shear, the nonequilibrium crystalline phase L c melts back to the equilibrium mesophase). This is different from the shear-driven crystallization below T o K , which is irreversible. Rheological optical observations show that the growth of the crystalline phase occurs through a preordering of the L i phase to an L α phase induced by shear flow, before the nucleation of the L c phase. Shear diagram of the L i phase constructed in the parameter space of shear rate ð_ γÞ vs. temperature exhibits L i → L c and L i → L α transitions above the equilibrium crystallization temperature ðT o K Þ, in addition to the irreversible shear-driven nucleation of L c in the L i phase below T o K . In addition to revealing a unique class of nonequilibrium phase transition, the present study urges a unique approach toward understanding shear-induced phenomena in concentrated mesophases of mixed amphiphilic systems.shear-induced phase separation | strongly binding counterions | coagels S hear is known to assist crystallization below the equilibrium freezing temperature in complex fluids like colloidal glasses (1, 2), dense granular suspensions (3), polymer melts (4, 5), micellar solutions of block copolymers (6), and multicomponent surfactant systems (7,8). Shear-driven crystallization is equally relevant for simple fluids like bulk metallic glasses (9), molecular liquids (10), and atomic systems (11). The general understanding is that shear lowers the energy barrier for nucleation and accelerates the growth of a stable crystalline phase from a metastable, amorphous/ isotropic solution at Peclet number Pe = σa 3 kBT > 1, where σ is the shear stress, a is the characteristic length scale, and k B T is the thermal energy (12). The crystalline phase primarily induced by the effect of flow on the internal structure and ordering of the constituents does not revert to the starting fluid state when the imposed shear is removed, indicating that the phenomenon is not a dynamic phase transition. In the present study, we report a unique phenomenon, where under steady shear, crystallization occurs above the equilibrium crystallization temperature ðT o K Þ in an isotropic mesophase ðL i Þ consisting of bilayers formed in a lyotropic surfactant system. Notably, above T o K , when the imposed shear is removed, the crystalline phase melts back to the starting L i phase.The studies were carried out in a cationic-anionic mixed surfactant system formed by SDS and the strong binding counter-ion paratoluene hydrochloride (PTHC) in water. At equilibrium, the organic counter-ion PTHC has the tendency to remain at the micelle-water interface, decreasing the spontaneous curvat...

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Melting and crystallization of colloidal hard-sphere suspensions under shear

Cited by 133 publications

References 56 publications

Aqueous Colloid + Polymer Depletion System for Confocal Microscopy and Rheology

Aqueous Colloid + Polymer Depletion System for Confocal Microscopy and Rheology

Assembly of vorticity-aligned hard-sphere colloidal strings in a simple shear flow

Reversible shear-induced crystallization above equilibrium freezing temperature in a lyotropic surfactant system

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